Fixed resistor



P 1962 J. G. RUCKELSHAUS 3,052,862

FIXED RESISTOR Original Filed June 7, 1952 INVENTOR. JOHN G. RUCK ELS HADS ATTORNEY United. States Patent and this application July 17, 1959,Ser. No. 827,935

2 Claims. (Cl. 338258) This invention relates to a resistor. Moreparticularly, this invention relates to a metallic film resistor of thesealed type, and having improved characteristics.

This application is a division and continuation-in-part of my copendingapplication, Serial No. 292,367, filed June 7, 1952, now issued as US.Patent No. 2,917,814, dated December 22, 1959.

An object of my invention is to provide a metal film resistance unitthat is stable and has a low temperature coefficient of resistance.

A further object of my invention is to provide a simple, low cost,sealed, precision metal film resistor.

One further object of my invention is to provide a sealed resistorcomprising an insulating tube whose interior is glazed with ametalliferous surface and has terminal conductors at sealed endsthereof.

An object of this invention is the provision of an improved resistorcomprising an insulating tube carrying metallic terminals at each end, ametallic resistance material on the inner wall of the tube and at leastpartially overlying each of the said metallic terminals, and end capsalfixed to the tube and making individual contact with the metallicterminals such that the metallic terminals act as electrical conductorsbetween the resistance material and the end caps.

Other objects and features of my invention will become apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of one embodiment of myinvention,

FIG. 2 shows a transverse section view of another embodiment of theinvention,

FIG. 3 is a longitudinal section takenon line 33 of FIG. 2,

FIG. 4 is a fragmentary, exploded, longitudinal sectional view showing amodified sealing means and a different form of the metallic resistancefilm.

Similar reference numbers refer to like parts throughout. Referring nowto FIG. 1, there is shown an insulator cylinder or tube 14 which may bemade of glass, ceramic or other suitable material adapted to hold ametallic film thereon and which is made of dielectric material. Saidtube is provided with recessed or undercut end portions 15 and thread16, said thread extending from one to the other of the recessedportions. Prior to forming the resistance film on the inner wall of thetube, the recessed end portions 15 are coated with a silver, or platinumor other metal paste or frit and baked or fired or heat treated therebyforming terminal bands 17 which are interfused with the dielectricmaterial forming the substrate. The terminal bands then may be maskedoff with any suitable paste, but leaving a portion exposed forcontacting with :a film to be formed.

The cylinder or tube 14 is then treated as described in the parentapplication whereby the helical thread 16 is formed and then coated witha metallic resistance film 18, such as Nichrome, preferably by anevaporation process as disclosed in the parent application. It is a wellknown physical law that when a filament such as Nichrome or some otheralloy is heated or lighted in a container encasing a high vacuum, themetal will evaporate or sublimate and deposit either on the inner wallsof the container or onto other objects which may be in said r 3,052,862Patented Sept. 4, 1962 vacuum. The amount of material evaporated orsublimated is in proportion to the heat of the filament and the lengthof time that the filament is heated or lighted.

The tops 19 of the film 18 are removed by reaming, this, forming ahelical ribbon of resistance material that overlies or spans each of theterminal bands 17. It is to be noted that the amount of reaming dependsupon the resistance value desired in the finished product or unit.Furthermore, in forming the helical metallic resistance film, theterminal bands are in good contact therewith.

After the interior of tube 14 has been prepared, metal end caps 20 aretightly fitted into the recesses 15, as shown, so that there is goodcontact between the thread or film 18, the band 17 and the cap 20. Saidend caps are then peripherally soldered to the terminal bands 17 asindicated by numeral 21. It is to be noted that there is provided a goodsoldered joint, since the outer portion of the terminal band was maskedwhich mask is removed prior to the installation and attachment of endscaps 20.

It is apparent that such construction results in a sealed unit whereinthe terminal bands 17 and 17 serve as good electrical connectionsbetween the associated metal caps 20 and the resistance film 16.

Connection leads 22 are provided for each end cap 20, being solderedthereto or otherwise being firmly con nected to each end capforconnecting the resistor into an electrical circuit.

In FIGS. 2 and 3, it will be seen that the cylinder or tube 14a haslongitudinal splines 23. Said splines when coated as described in myparent application provide a desired ohmage or resistance. The ends ofthe tube 14a are shown as not being recessed although they may be asshown in FIG. 1. The terminal portions 24 and 25 may be initiallytreated with a silver or platinum or other metal paste and fired orbaked, and then coated with a resistance film according to my inventiondescribed hereinabove. The resistance of the splined tube is determinedand end caps 20 are connected and soldered at 21 as shown. Furthermore,the end caps 20 are each provided with connection leads 22.

In the modification shown in FIG. 4, it will be noted that the insidewall or interior 26 of tube 27 is provided with a continuous film 28.Also, the terminal portions 29 of the tube are provided with a coatingof silver or platinum or other metal on both the inside and outside ofthe ends of the tube. This can be done by dipping each end of the tubeinto a paste to the proper depth or the paste can be brushed on to forman annulus 30, preparatory to baking the tube. The tube may then besealed, after having determined its ohmage, by using end caps 31 whichare shown to pass over the periphery of the end of the tube to contactthe silver or platinum or other metal end thereof. Said caps 31 areadapted to fit tightly over the ends 29 of the tube.

In addition to the above metals, I may employ pure metals or alloysthereof for coating the cylinders or helices above indicated. It hasbeen found that a pure Nichrome alloy, free of impurities such as ironand/or aluminum, has produced a very stable unit or resistor.

It can readily be seen that many resistors can be prepared in batch formsince many tubes can be strung onto one fixture, and coated so as tocreate several resistors at a time. These resistors can be removed andchecked, thus economically forming stable metal film resistors ofextremely low temperature co-eificient of resistance. In this case, theends can be filled with a casting material, such as is shown in FIGS. 1,3 and 4 in order to seal the resistance element. Furthermore, the endsof the cylinder 14 may be initially provided with end terminals bakedthereon, namely on the inside, the ends and the outside so that an endcap can be readily added thereon.

Instead of accurately evaporating the metal, metal can be deposited to avalue lower than required, then, by connecting the unit across aWheatstone bridge or similar apparatus, careful adjustment of the unitcan be made by the amount of material cut or reamed off. This unit canthen have lug or wire terminals attached to each end and sealed, or ashaft carrying a moving contact can be inserted so that the unit can beused as a potentiometer or rheostat.

In accordance with my invention the resistor is made by first threadingthe interior of tube '14, and then may be undercut as shown in FIG. 1 tothe depth of the thread. The cylinder is then glazed and fired, duringwhich the undercuts are coated with silver, platinum or other metalpaste up to and including the thread ends. If desired the platinum orother metal paste may extend over one or more of the adjacent threads toinsure proper connection. The cylinders are then fired and baked. Nextthe alloy is then evaporated into the interior of the tube, firstmasking oil? the undercut with platinum so that the alloy film contactsplatinum on first and last thread in the cylinder. The thread is cut orreamed to the desired resistance as shown, by a Wheatstone bridge orother suitable instrument. Once the desired ohmage has been obtained,caps carrying their respective lead wires, are forced into therespective undercuts or over the end and solder applied to the platinumto seal the unit.

Furthermore, it will be noted that, by my invention, I provide aresistor having a film of nickel-chrome alloy deposited on the innerwall of aglazed or unglazed ceramic, glass or similar type of tube onwhich a metal tenminal material has been baked or otherwise deposited ateach end. Furthermore, there is provided a ceramic tube in which grooveshave been cut either in the form of a helix or parallel splines havingmetal terminals deposited at each end of the tube so as to form aresistance path between the metal terminals. The metal film may beremoved from the inside diameter of the grooves or threads so as to formthreads of resistance material in 'one case and parallel resistancepaths between the metal terminals in the second, said removal beingdependent upon the amount of resistance desired or needed, but

approximately the same amount of material will always be removed fromall parts.

It is to be noted that I may use any dielectric material suitable forthe purpose intended such as ceramic, porcelain, glass, Alundum, all ofwhich may be glazed or unglazed.

Also, a resistor is provided having metal end terminals forced into theends of tubes and electrically connected to the terminal bands so as toform a hermetically sealed resistor unit inside of the tube.

While preferred emobdiments of my invention have been illustrated anddescribed, it is to be understood that modifications as to form,arrangement of parts and use of materials may be made without departingfrom the spirit and scope of the invention as claimed herein.

I claim:

1. A resistor comprising an insulator tube, metallic terminals on eachend of the tube interfused therewith, a helical, metallic resistancefilm on the inner wall of said tube and overlaying at least a portion ofeach terminal, said film consisting of a nickel chromium alloy bonded tosaid wall and terminals, and metallic end caps aflixed to said tubemaking electrical contact with said terminals and sealing said tube,said terminals acting as electrical connectors between the resistancefilm and the end caps.

2. A resistor acocrding to claim 1, in which said terminals are selectedfrom the group consisting of platinum and silver.

References Cited in the file of this patent UNITED STATES PATENTS1,739,256 Peuder et a1. Dec. 10, 1929 2,037,951 Thomson Apr. 21, 19362,547,405 Mitchell et a1. Apr. 3, 1951 2,557,983 Linder June 26, .19512,569,773 Orr Oct. 2, 1951 2,586,752 Weber et a1 Feb. 19, 1952 2,792,620Kohring May 21, 1957 FOREIGN PATENTS 61 1,250 Great Britain Oct. 27,1948

